520 Web server is returning an unknown error
HTTP response status code 520 Web server is returning an unknown error is an unofficial server error that is specific to Cloudflare. This is a catch-all error that is used in the absence of having a HTTP status code for one that is more specific.
Cloudflare is a content delivery network that acts as a gateway between a user and a website server. When the 520 Web server is returning an unknown error status code is received, it can mean one of several things:
It can indicate that something unexpected happened with the origin server.
The origin server incorrectly interprets the HTTP request.
The origin server is unwilling to process the HTTP request due to a HTTP protocol violation or an empty response.
The 520 Web server is returning an unknown error status code is a Cloudflare-specific server error that is generated because the origin server response is empty, unknown, or unexpected.